1. Technical Field
The present invention relates to an ultrasonic diagnosis apparatus, and more particularly to a technique of reducing an unnecessary or undesired signal component such as a side-lobe component, a grating lobe component, or the like, contained in a reception signal.
2. Background Art
Ultrasonic diagnosis apparatuses are apparatuses which form an ultrasonic diagnosis image by transmitting and receiving ultrasound to and from a living organism. In order to increase the image quality of the ultrasonic diagnosis image, it is desirable to reduce an unnecessary signal component contained in a reception signal; i.e., a side-lobe component, a grating lobe component, a noise component, or the like.
More specifically, in a receiving beam former provided in an ultrasonic diagnosis apparatus, for the purpose of focusing, delay processing (phase alignment processing) is applied to a plurality of element reception signals supplied from a plurality of transducer elements, and thereafter, summing processing is further applied to the plurality of element reception signals having been subjected to the delay processing. With these processing operations, beam data serving as an RF signal, for use in forming an ultrasonic image, are obtained. When reflection waves are received from a focus point, as phases are identical among the plurality of element reception signals having been subjected to the delay processing, beam data having large amplitude can be obtained after the summing processing. In contrast, in the case of reflection waves from a point other than the focus point, as the phases are not identical among the plurality of element reception signals, only beam data having low amplitude can be obtained. However, the beam data actually contain an unnecessary signal component such as a side-lobe component.
As a method for suppressing an unnecessary signal component contained in a reception signal, a method for suppressing a reception signal by using a factor, called SCF (Sign Coherence Factor), has been proposed. According to this method, based on a sign data array which is formed of a plurality of sign data items arranged in the element arrangement direction, which are extracted from a plurality of element reception signals having been subjected to the delay processing but having not yet been subjected to the summing processing, the gain of a reception signal (beam data) after the summing processing is adjusted. Specifically, the gain is adjusted in accordance with SCF, which is defined based on the ratio of the number of positive sign data items and the number of negative sign data items (see Jorge Camacho, et al, “Phase Coherence Imaging”, IEEE Transactions Ultrasonics, vol. 56, No. 5, 2009 (WO2010/018282)).
However, if the SCF method described above is always applied, there may be a possibility that a main lobe component is excessively suppressed, thereby reducing the image quality of an ultrasonic image. Specifically, according to the above SCF method, in which only the number of positive sign data items and the number of negative sign data items are referenced, the gain control is not based on the amplitude of the individual element reception signals and the amplitude profile formed of a plurality of instantaneous amplitude values of the plurality of element reception signals. Accordingly, with the SCF method, there is a possibility that turbulence of the phase is misidentified when the amplitude profile changes across the baseline, despite the amplitude profiles being identical to a certain degree.